Thermal Properties of Calamus Deërratus, Raphia Hookeri And

Short Communication

Thermal properties of Calamus deërratus , Raphia hookeri and synthetic board in building design in Southwestern Nigeria

Alausa S. K.1, Oyesiku O. O.2*, Aderibigbe J. O.1 and Akinola O. S.1

1Department of Physics, Olabisi Onabanjo University, Ago-Iwoye, Ogun State, Nigeria. 2Department of Plant Science and Applied Zoology, Olabisi Onabanjo University, Ago-Iwoye, Ogun State, Nigeria.

Accepted 16 March, 2011

For a self-cooling building, alternative sources of roofing and ceiling materials in building design was investigated. The thermal property of Rattan palms (Calamus deërratus ), Raffia palms (Raphia hookeri) and synthetic Nigerite asbestos sheets were determined using the Lees’ disc apparatus. Results showed that Rattan palms sheet had the lower thermal conductivity (k = 0.046 Wm -1 K-1) and a higher resistivity (r = 21.930 W-1mK) compared with Raffia palms sheet. While both palms showed lower thermal conductivity (k = 0.046 to 0.056 Wm -1K) and higher resistivity (r = 17.73 to 21.930 W-1mK) than asbestos sheet (k = 0.084 Wm -1K, r = 11.919 W-1mK). The results indicated that Rattan palms have a higher potential for heat resistivity than many other wood based heat-insulating materials and are recommended for ceiling in modern building design.

Key words: Self-cooling building, insulators, heat, Lees’ disk, Rattan, Raffia.

INTRODUCTION

In tropical region, with reference to Nigeria, materials like Southwestern Nigeria can be taller than 16 m with large zinc, aluminum and asbestos are commonly used in form green shining fronds and curved spadices branching to of sheets for roofing in modern building constructions, but form numerous hanging partial inflorescences. Trunk of these materials have a high ability to conduct heat (solar R. hookeri is a very useful source of building material and radiation) into the interior space of a building, a situation the local people in Nigeria tap wine from the living trunks that causes discomfort in indoor space in dry season. (Hutchinson and Dalziel, 1963). The heat generated indoor depends solely on the rate of Rattan palms ( Calamus deërratus Mann and Wendl) heat conducted through the building materials used for commonly called nasty palms, is a monocotyledonous the construction. Besides, the heat flow through any plant in the Arecaceae family. Mature Rattan is similar to building material is dependent on the thermal properties bamboo (Bambusa vulgaris ) but the stems are solid of the material (Akpabio et al., 2001). The need for the rather than hollow as found in bamboo. Rattan palm is self-cooling building has resulted in the search for fast growing and distinct from other palms due to its alternative sources of roofing and ceiling materials with slender sheathed stem (1.8 - 3.0 cm diameter) with long suitable building construction properties. Rattan and internodes similar to bamboo, between the leaves when Raffia palms are one of such. matured. Rattan leaf-sheath often thickly armed with Raffia palms (Raphia hookeri Mann and Wendl) is a straight spines (4 - 5 cm). Leaves (1 m long) are solid straight monocotyledonous plant belonging to the arranged distant from each other (2.5 cm). Lower surface family Palmae, and with trunk covered with an attractive of the leaves have fine slender and tapering spiny vine- unusual coils, and occasionally producing suckers. A like hooks. Spiny vine-like hooks aid leaves to scramble typical full-grown R. hookeri of the forest zone in through and over other plants to the tree canopy for light. Leaves rachis is armed with sharp recurve hooks ending in a slender tentacles (cirrus); long, slender spadix, tapering to a fine flagellum armed with recurve thorns, *Corresponding author. E-mail: [email protected]. and partial inflorescences, bearing flowers branchlets

282 Afr. J. Plant Sci.

Table 1. Thermal resistivity and conductivity of Rattan ( Calamus deërratus ), Raffia ( Raphia hookeri ) palms and Asbestos board.

Sample Thermal resistivity [W -1mK (r)] Thermal conductivity [(k) Wm -1K] Calamus deërratus 21.930 0.046 Raphia hookeri 17.730 0.056 Asbestos sheet (Nigerite) 11.9190 0.084

(5 cm long). Flowers are singles in male spadix, and trimmed into a circular size of brass disc of a Lees’ disk with paired in the fruiting female spadix, with a male or neuter diameters of (y = 110 mm) (Nelkon, and Ogborn, 1985). in the same small bract (bracteole). A fruit shape is oblong-ellipsoid, pointed (1.5 cm long), with 16 – 21 Methods vertical rows of triangular-ovate, and fringed (fimbriate) scales (Hutchinson and Dalziel, 1963). The thermal conductivities of the palms and the asbestos were The attributes of Rattan, lightweight, durability, flexibility determined for each sample using the Lees’ disc apparatus (Ekpe, and resistant to splintering makes it a very good material and Akpabio, 1994; Nelkon, and Ogborn, 1985). Each sample in turn was inserted between the brass hollow cylinder, and brass slab for building construction. Akpabio et al. (2001) studied the of Lees’ apparatus, and the brass base was fitted to steam chest. thermal properties of some palms fibers and established Steam was passed into the apparatus and temperatures T1°C and that Raffia palms fibers are good thermal insulators. T2°C were recorded at a steady state. The brass hollow cylinder There is no report on thermal properties of Rattan palms and the samples were removed and the brass slab was heated known to the authors. directly on the heating chamber until its temperature was 5°C The process of conduction and radiation often generate higher than that recorded in the steady state. The heating chamber was removed to allow the brass slab cooled down and the heat experience in interior spaces via the roof and walls. temperature readings were taken at interval of 30 s until the The radiation transport is strongly dependent on tem- temperature fell to 5°C below the steady state temperatures. perature and particularly significant at high temperatures. The convention can be negligible for small pore sizes (Akpabio et al., 2001). The temperature variation with Calculations thickness of a solid material determines if a material is The cooling-curve was plotted and the gradient was determined suitable as heat insulator or conductor. The actual heat from the temperature data obtained. Thermal conductivity was transmission by conduction depends on the bonding determined using Nelkon and Ogborn (1985) equations. between molecules (Collieu and Powney, 1977). The theory therefore is, the rate of heat flow in dry solid KA (θ − θ ) dθ H = 1 2 = mc (1) material is proportional to the area ( A) of the part x dt perpendicular to the direction of heat flow and

 − dθ  Thus, temperature gradient at that section   and the  dx  mcx dθ properties (nature) of the material. K = (2) This work was aimed at comparing thermal properties A()θ − θ dt 1 2 of Rattan and Raffia palms and in turn with that of synthetic asbestos and to make recommendation on the Where H is the rate of heat flows; m is the mass of the brass slab; c best material for modern building constructions. is the specific heat capacity of the brass slab; x is the thickness of each sample; A is the cross-sectional area of the sample; dθ (θ −θ ) is the difference in the steady state temperature; MATERIALS AND METHODS 1 2 dt

Collection and preparation of samples is the gradient from the cooling curve; K is the thermal conductivity.

Fresh Rattan and Raffia palms used were harvested from the green reserve forest located at “The Biome” of Olabisi Onabanjo RESULTS AND DISCUSSION University Ago-Iwoye (Lat 6°55´ 55´´N, long 3°52´ 58´´E elevation of 30 m). The asbestos sample was collected from works and The results of thermal properties of the three kinds of services of the university. The Rattan and Raffia palms samples ceiling materials were shown in Table 1. Rattan sheet were sliced into equal uniform thickness (x = 3.0 mm). Both palms samples together with asbestos sheet were oven dried to constant (Calamus deërratus ) exhibited the least thermal weight. The dried Rattan and Raffia palms samples were weaved conductivity and the most thermal resistivity among the into a small mat. Both palms together with the asbestos sheet were other materials tested. The fact that the rural people of

Alausa et al. 283

Table 2. Thermal resistivity and conductivity of wood-based heat insulating materials (Agarwal, 1967; Akpabio et al., 2001; Ekpe and Akpabio, 1994; Etuk et al., 2005).

Material Thermal conductivity ( k) W -1mk Thermal resistivity [(r) W -1mK] Asbestos board 0.319 3.135 Brick building 0.600 1.666 Pine fiberboard 0.052 19.230 Pine wood 0.138 7.246 Oak wood 0.160 6.250 Coco nucifera 0.121 8.264

Nigeria use Rattan and Raffia palms for making chairs, ACKNOWLEDGEMENTS tables, hats, and mats for use, particularly in the hotter part of the country, corroborate the structural suitability and durability of these materials. The high resistivity of The authors are grateful to Yu Ning-ning and Yu Sheng- heat found in the Rattan and Raffia palms when xian of the herbarium, Institute of Botany, Chinese compared to the asbestos makes it cheaper and portable Academy of Science, for their help. Appreciation also materials in the design of a self-cooling building. goes to the Department of Physics, Olabisi Onabanjo The results in this work (Table 2) were compared with University for the use of the laboratory facilities. the data values published by previous investigators for other wood-based materials used for heat insulation (Agarwal, 1967; Akpabio et al., 2001; Etuk et al., 2005; REFERENCES Twidell and Weir, 1990). The range of thermal -1 -1 Agarwal KN (1967). Thermal Data of Building Fabrics and their conductivity (k) values (0.04 - 0.08 Wm K ) determined Application in building design, Building Digest No. 52, Roorkee, India: in this work were far lower than the range of values (0.05 Central Building research Institute. Digest, No. 52 - 0.32 Wm -1K-1) published for other commonly used Akpabio LE, Ekpe SD, Etuk SE, Essien KE (2001). Thermal Properties materials for heat resistance (Etuk et al., 2005). However, of Oil and Raffia Palm Fibrers, Global J.Pure Appl. Sci., 7(3): 575- 578. Raffia and pinewood had similar conductivity (k) values. Collieu AMB, Powney DJ (1977). The Mechanical and Thermal Of the three materials tested in this work, only the Properties of Materials. London: Edward Arnold. p. 283. asbestos resistivity (r) value was within the range of Ekpe SD, Akpabio GT (1994). Comparison of Theremal Properties of values (0.74 - 16.13 W-1 mK), while the Rattan and Raffia Soil Samples for a Passively Cooled Building Design. Trad. J. Phys., 18:117-122. values were well above the published range for Etuk SE, Akpabio LE, Akpabio KE (2005). Determination of thermal commonly wood-based insulating materials used for properties of Cocos nucifera trunk for predicting temperature variation buildings (Agarwal, 1967; Akpabio et al., 2001). within its Thickness. The Arabian J. Sci. Eng., 30(1A): 121-126. Therefore, Rattan palms plantation for domestic building Hutchinson J, Dalziel JM (1963). Flora of West Tropical Africa lll (ii) Monocots. Crown Agents for Oversea Governments and material as well as for exportation should be encouraged. Administration. London, p. 131. If implemented, it will serve as an alternative to timber Nelkon M, Ogborn JM (1985). Advance Level Practical Physics. 4 th resources, thereby improving the economic situation of edition, Heinemann Educational Book, p. 67. individuals and ameliorate the rate of deforestation due to Twidell J, Weir T (1990). Renewable Energy Resources. London: E and F.N Spon, pp. 418. lumbering of timber for building materials.

Conclusion

From the fore-going experimental results, the Rattan palms of all the three materials tested had the lowest thermal conductivity resulting in high thermal resistivity that favours it as an interior building insulating material for naturally cooled building design in tropical countries.